This invention relates to a device for preventing vibration caused to a rotation shaft of a disc drive motor for rotating a disc in a disc playback device.
In a disc playback device for playing back a disc such as a laser disc and a disc of the Compact Disc Digital Audio System, a turntable on which a disc is placed and rotated is connected to a rotation shaft of a disc drive motor and the disc is driven by a system called a direct drive system.
The disc drive motor used for this type of disc playback device is generally so constructed that there is room for its rotation shaft to move in both radial and axial directions. In this type of disc playback device, therefore, the rotation shaft of the disc drive motor sometimes vibrate radially or axially during playing back of a disc with a result that the disc is radially or axially displaced. If the disc playback device is of a type which reads signals recorded on the disc by an optical system, and excessive load is applied to a tracking servo system or a focusing servo system of the device so that there is the likelihood that accurate reading of signals can no longer be achieved.
For eliminating the disadvantage caused by the vibration of the rotation shaft of the disc drive motor in radial direction, there have been provided devices for imparting a side pressure to the rotation shaft as shown in FIGS. 5 and 6.
The prior art side pressure imparting device shown in FIG. 5 includes a disc drive motor 1, a fixed pin 2 and an engaging member 3 provided in the vicinity of the disc drive motor 1. A spring 4 is wound on the fixed pin 4 and one end portion of this spring 4 is on abutting engagement with the engaging member 3 and the other end of the spring 4 is in abutting engagement with a rotation shaft 5 of the motor 1. According to this device, a side pressure is imparted to the rotation shaft 5 by the urging force of the spring 4.
The prior art side pressure imparting device shown in FIG. 6 includes an arm 7 provided in the vicinity of the disc drive motor 1 which are 7 is pivotable horizontally about a pin 6. A roller 9 is mounted in the forward end portion of the arm 7 so that it is rotatable about a pin 8. The arm 7 is pulled by a spring 10 to press the roller 9 against the rotation shaft 5 of the motor 1. According to this device, a side pressure is imparted to the rotation shaft 5 by the pressing force of the roller 9.
These prior art devices aim at preventing undesired displacement, i.e., vibration, in the radial direction of the rotation shaft 5 of the motor 1 by imparting a side pressure to the rotation shaft 5. These devices, however, have the disadvantage that, since the spring 4 or the roller 9 is in abutting engagement with the rotation shaft 5, vibration applied to the spring 4 or the roller 9 from outside of the device is directly transmitted to the rotation shaft 5 so that the rotation shaft 5 tends to be adversely affected by the vibration transmitted from outside of the device. Besides, when the devices have been used for a relatively long time, portions of the rotation shaft 5, the spring 4 and the roller 9 which are in contact with each other are worn away with resulting deterioration in the side pressure imparting function.
For preventing vibration of the rotation shaft in the axial direction, it is conceivable to achieve it by increasing accuracy of machining of the disc drive motor components. It is actually not possible to eliminate the vibration in the axial direction totally by this approach.
A device as shown in FIG. 7 has previously been proposed in the U.S. patent application Ser. No. 658,226 by the same assignee. In FIG. 7, reference numeral 11 designates a chassis. A main body 13 of a disc drive motor 12 projects downwardly from the lower surface of the chassis 11. A turntable 15 is connected to a rotation shaft 14 of the motor 12 projecting upwardly from the upper surface of the chassis 11. Above the turntable 15, there is provided a clamper 17 for clamping a disc 16 between it and the turntable 15 when the disc 16 is placed on the upper surface of the turntable 15. In the clamper 17, a rotary plate 19 is rotatably supported on the lower surface of the forward end portion of a clamper main body 18. The clamper 17 is normally spaced from the turntable 15 and, when the disc 16 has been placed on the disc 16, the rotary plate 19 is urged downwardly by force of an unillustrated spring to clamp the disc 16 on the turntable 15. According to this disc playback device, since the disc 16 and the turntable 15 are urged downwardly by the clamper 17 when the disc 16 has been placed on the turntable 15, the rotation shaft 14 also is urged downwardly so that vibration of the rotation shaft 14 in the axial direction can be prevented.
In this prior art disc playback device in which axial displacement of the rotation shaft 14 is made by the urging force of the clamper 17, vibration applied to the clamper 17 from outside is directly transmitted to the rotation shaft 14 so that the rotation shaft 14 tends to be adversely affected by the vibration applied from outside.